The present invention relates to thermally conductive elastomeric pads and methods for manufacturing such pads. Particularly, the pads comprise an elastomer polymer matrix and a thermally conductive filler material. The pads produced by these methods can be used as thermal interfaces to dissipate heat from heat-generating electronic devices.
Electronic devices such as semiconductors, microprocessors, and circuit boards can generate a substantial amount of heat that must be removed in order for the device to function properly. The industry uses thermally conductive compositions to dissipate heat from such electronic components. Typically, such compositions comprise a base polymer matrix and thermally conductive filler material.
For example, Peterson, U.S. Pat. No. 5,011,870 discloses thermally conductive organosiloxane compositions comprising a polyorganosiloxane and a mixture of thermally conductive fillers that includes aluminum nitride.
McCullough, U.S. Pat. No. 6,251,978 discloses a thermally conductive composition comprising a polymer base matrix (liquid crystal polymer) and thermally conductive fillers (aluminum, alumina, copper, magnesium, brass, carbon, and boron nitride).
Conventional thermally conductive compositions can be used in a variety of ways. For example, a heat-generating device (e.g., electronic part) and an adjacent heat-dissipating article (e.g., heat sink) first are secured in place by mechanical means using clips or screws. Thermally conductive pastes or greases comprising polysiloxane oils loaded with fillers are then smeared onto these components. The thermally conductive greases tend to have initially good film-forming and gap-filling properties. For example, small gaps may exist between the heat sink and electronic part, where these components interface with each other. The uneven mating surfaces of these components can cause such gaps. The thermal greases tend to seep into these gaps bringing the heat sink and electronic part into initial contact with each other. However, it has been found that such thermal greases have poor adhesive properties and will ultimately seep out. This seepage causes air voids to form between the two surfaces resulting in hot spots. Moreover, the mechanical fasteners may exert excessive pressure on the heat sink and accelerate the seepage. It has been reported that seeping polysiloxane oils can evaporate and re-condense on sensitive parts of surrounding microcircuits. The re-condensed oils lead to the formation of silicates that can interfere with the microcircuits and cause the microprocessor to fail in operation.
In the case of polysiloxanes and thermoplastic polymers, these materials are typically cast in sheet form and die-cut into desired shapes corresponding to the shapes of the heat sink and heat-generating device. The resulting pre-formed sheet is attached to the surface of the heat-generating device, and the heat sink is secured by means of clips or screws. These pre-cut, thermally conductive sheets solve the problems associated with the above-described greases. However, an operator may find it difficult to precisely cut the sheets to specific configurations. Thus, the sheets may not have the proper geometry to provide an optimum pathway for heat-transfer between the heat-generating device and heat sink. Further, the added step of cutting and manually applying the preformed sheets adds cost to the assembly process. The sheets may have non-uniform thickness and vary in their effectiveness to transfer heat. Finally, while these sheet materials are suitable for filling undesirable air gaps, they are generally less thermally conductive than the heat sink member. Thus, these sheets can detract from the overall thermal conductivity of the assembly.
In view of the foregoing problems, it would be desirable to have a method for making a thermally conductive elastomeric pad, where no further processing or tooling is required to produce the final shape of the pad. In addition, the pad should be capable of providing a tightly conforming interface between heat-generating and heat-dissipating devices. The present invention provides such an elastomeric pad and the methods for making such a pad.